Human-Structural Interaction for Stationary Human Whole-Body in Vertical Structural Vibration

Abstract

The dynamic properties (natural frequencies and damping ratios) of the stationary human body were mainly studied in human body biomechanics and those for the first mode of vibration of a standing human body were determined experimentally by conducting human-structural interaction (HSI) tests. This thesis first time to determine the first two natural frequencies and damping ratios of the standing and sitting human bodies by taking human-structural interaction experiments. A structure-shoe-human body model has been developed to provide the possibility for designing vibration-reduction shoes. The basic formulas for three degree-of-freedom (3DOF) HSI models are derived and the theoretical expressions of the acceleration Frequency Responses Functions (FRFs) are validated using the Newmark-β and Euler Integration methods. The dynamic parameters of the SDOF and the 2DOF human body interaction models are determined using the available biomechanics experimental results. It demonstrates that the 2DOF human body interaction model is the best among all biomechanics body models and HSI models. A group of 26 healthy human subjects were tested individually in standing and sitting postures on a test rig that behaves as a SDOF structure. All the experimental FRF curves show clearly two or three resonance frequencies, which are obtained from the measured acceleration of the occupied test rig. The dynamic properties of the human body are identified by best fitting between the experimental and theoretical FRFs, The averages of the first two natural frequencies of the standing human body are 5.67Hz and 15.86Hz and the damping ratios are 0.31 and 0.25 respectively, whereas those for the sitting human body are 5.40Hz and 9.36Hz and 0.25 and 0.11 respectively. There are no significant differences in the dynamic parameters of the first mode for the standing human body between using the 2DOF and the 3DOF HSI models. A 3DOF human-shoe-structural interaction model for the standing human body is developed and the shoe was treated as a spring-mass-damper model between the human body and the vibrating structure. The ranges of the vertical stiffness of shoes are calculated to achieve at least 50% vibration reduction on the human body. The presence conditions of the two resonance peaks for the 2DOF HSI model for the standing human body are determined as a function of the mass and natural frequency ratios (human body to structure) and the human body damping ratio. The presence areas of the 2DOF conventional model are smaller than that of the 2DOF HSI model. The relative human body vibrations to the vibrations of the occupied structure and to the empty structure are presented based on the dynamic parameters obtained from the above HSI experiments. The results show that the human body responses could be 2-3 times that of the occupied structure and that of the empty structure subjected to the same harmonic loading.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Tianjian Ji (Supervisor) & Parthasarathi Mandal (Supervisor)